My Speer Reloading Manual, 11th edition, lists round ball loads for the .45 Colt. "Loads shown for the SPEER lead round ball are intended for use as gallery, or short range target loads. Accuracy can be quite good out to 50 feet."
They specify a .454 diameter ball of 141 grains. It's loaded very low, to under 600 fps.
I presume you could do the same thing with black powder instead of the smokeless the Speer manual specifies. Probably have to seat the ball deep within the case over a reduced powder charge? It seems to me that if you followed safe reloading practices, the worst that could happen would be a batch of inaccurate cartridges. But I am not sure, so I will defer to the experts on that.